The present invention relates to a method for operating an automation system with a plurality of communication users connected for communication purposes via a serial link.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
In an automation system which is normally operated as a real-time system, with a plurality of modules functioning as communication users in the communication system, there is the need to synchronize these communication users in order to make simultaneous working possible. When the communication users are not supplied with a system-wide clock, as is expedient and normal for greater distances, a jitter inevitably arises which is of the order of magnitude of one clock period, with which the communication users are each clocked internally and a synchronization signal is produced by the synchronization.
Automation systems of the aforedescribed type and methods for their operation are known in the art. The disadvantage, however, in a serial transmission of a synchronization signal is the inevitable jitter which additionally arises during said transmission. This occurs through the serial protocol not usually being able to be sent at just any time. The reasons for this can be that the synchronous signal can only be sent and thereby the receiver or each receiver can only be notified when a data transmission in progress is completed. Furthermore, the baud rate of the transmission is low compared to the respective module clock even when it is expediently formed by a fixed divisor from the respective module clock. Finally, the signal is transmitted by data symbols which, although they are likewise formed by a fixed divisor from the system clock, overall let the duration of the data transmission compared to the respective module clock be of a comparatively long duration.
It would therefore be desirable and advantageous to obviate prior art shortcomings and to provide an improved method for operating an automation system in which, for transmitting a synchronous signal between communication users included in the automation system, of which at least one communication user functions as a sender and at least one other communication user functions as a receiver, to avoid the above disadvantages or at least to reduce their effects.